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Earth Analog Day

April 22, 2013

In 2008, California ran a profile of Natali Batalha ’89, Kepler mission scientist at NASA’s Ames Research Center. So when NASA announced Thursday that it had discovered a slew of new worlds among the stars, including Kepler-62f, the most Earth-like planet yet, we called her up to fill us in on this latest development. [Image credit: NASA Ames/JPL-Caltech]

“This is what Kepler was built to do. It was expected that we would find planets like this. That said, it’s very exciting,” Batalha said. “This is the closest thing we have to an Earth analog.”

But what do we mean when we say a planet is Earth-like? Skies of blue, clouds of white, and the reincarnation of Louis Armstrong? Well, that’s the best-case scenario, obviously, but we don’t yet have the instruments to tells us about the planet’s atmosphere nor to detect legendary hornmen. What we can detect (or infer—there’s a lot of inferring) so far is the size, mass, density, and temperature of a planet. When we say “Earth-like,” we’re looking for a rocky planet orbiting inside a star’s so-called Goldilocks region—at a distance that’s neither too hot nor too cold—where a planet might be host to liquid water.

The Kepler space telescope trails along behind us in the path of Earth’s orbit around the sun. It watches for stars to dim, evidence that a planet is orbiting that star, passing between it and us. By timing these transits, we can use the star’s mass to determine the planet’s orbital distance using Kepler’s third law of planetary motion. (Yes, he of the telescope.)

Mass we infer from studies of similar-size rocky planets. And that gets us density.

Here’s what we believe know about Kepler-62f, so far: It’s only 40 percent larger than Earth and, judging by its orbit, there’s a good chance it’s neither seared dry nor frozen solid. Oceans? Life? Jazz? We don’t know yet. But we can’t rule them out, so this is very exciting. Feel free to whistle the Star Trek theme.

Batalha says we’ve only analyzed about half of the data Kepler has collected since its launch four years ago and she fully expects that we’ll find even more interesting worlds in the data yet to be sorted—and the data Kepler has yet to record.

“The Kepler spacecraft is still up taking data and doing its thing and transmitting that data back to Earth. The longer we observe, the more planets we will find. We will gain sensitivity to the most [promising] region of parameter space, the parameter space that captures these Earth twins,” Batalha said. “We expected to see our most interesting planet candidates, these Earth twins, in later years of the mission and that’s now. That’s now. We’re collecting that data right now and really looking forward to seeing what it contains.”

—Brendan Buhler

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